I suggest you send it to RCBS in Oroville, CA. They can positively identify it for you. It seems that I recall the existance of various type dies in semi-auto cals. I believe these were termed 'small base' dies, the idea being that they sized the brass down smaller at the base so it would feed reliably in semi-autos. These type dies would over size the brass for bolt actions.

Thus, it seems to me you need a qualified opinion on just what it is you have. Walt

As I recall it is a sizing die that supposedly resizes cases in such a way that case trimming is virtually eliminated. I would give RCBS a call and ask for the instruction manual. They'll probably ship it to you for free.

Just got one of those X-dies myself in .223. Haven't used it yet, but what it does, is it stops the growth of the fired case. You must trim your brass prior to using the X-die, but the instructions say that it is the only time you will have to do this. Call RCBS, and they will send you the instructions. They are excellent about that.

Don't know there number off the top of my head, but it is an 800 number, check a gun magazine.

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